Method for injecting foam drilling fluid



T. L. COX

Filed Nov. 13. 1967 224.7 ZOTPQN-,Z-

METHOD FOR NJECTING FOAM DRILLI'NG FLUID Feb. 3, 1970 u. Z DI JQQMU lNvENTon.

THOMAS l.. cox

ATTORNEYS United States Patent O U.S. Cl. 175-24 3 Claims ABSTRACT OF THE DISCLOSURE A method of providing a drilling fluid in which the drill fluid is formed by injecting a liquid foam mixture into a stream of air. The air flow is maintained at a substantially constant rate by a valve which discharges air to the atmosphere in response to pressure differential across a venturi in the air stream.

BACKGROUND OF THE INVENTION The use of rotary drilling as a means of drilling oil and gas wells is well known. The drilling process includes rotating a drill string having affixed at the lower end thereof a bit which is rotated in contact with the earth engaged at the lower end of the hole, the bit serving to chip away the earth formation as the hole is advanced. All such rotary drilling require some drilling fluid medium. The most common medium is a water base drilling fluid medium which is circulated down the interior of the drill string, out the bit and up to the earths surface in the annulus formed by the bore hole and the exterior of the drill string. The drilling uid has several functions. First, and most important, the drilling fluid medium functions to carry the cuttings loosened by the drill to the earths surface where the cuttings are discharged permitting the drill bit to advance without impairment. Second, the drilling fluid medium cools the bit to prolong the life thereof. Third, lubrication of the bit is provided.

One difficulty with water or other liquid base drilling mediums is that in deeper holes the hydrostatic weight of the fluid becomes very great and applies a hydrostatic pressure to the earth formation so that the formation is continually drilled under compression. This has the effect of reducing drilling efficiency and at the same time causes a higher rate of bit wear.

In more recent years air has been utilized as a drilling medium. Air is forced down into the hole in the same way as the uid base drilling fluids and passes out through the bit and back up the annulus. Air has the great advantage that a greatly reduced hydrostatic force is applied to the formation so that improved drilling eiciency and longer bit life are obtained. One disadvantage, however, with air drilling is that a high volume of air must be pumped into the hole to maintain suicient rate of flow to carry the cuttings from the bottom of the hole to the top. The expensive equipment necessary to provide the high rate of air flow, particularly for deeper wells, has limited the use of air as a drilling medium.

SUMMARY OF THE INVENTION This invention combines the advantages of both liquid and air drilling and provides a method of providing a drilling medium for use in drilling of oil and gas wells consisting of a stiff foam.. The foam is injected into the interior of the drill string and passes down through the drill string, out through the bit, and back up through the annulus in the same way that both liquid and air drilling mediums have previously been used.

Advantages of the foam drilling medium of this invention are: (1) the hydrostatic pressure on the formation ice is 10W, that is, it is only slightly greater than when using air and much less than when using liquid drilling medium; (2) a high drilling rate and increased bit effectiveness is obtained; (3) the stiff foam drilling medium of this invention requires an air consumption rate of only a fraction of that for air drilling since the foam functions to assist in carrying the cuttings from the bottom of the hole and upward in the annulus to the earths surface; (4) the foam effectively lubricates the drill bit; and (5) since a relatively small volume of air is required the expense of the equipment for drilling a given size well is greatly reduced over that of using air alone.

DESCRIPTION OF VIEWS The figure is a block diagram showing the components of the apparatus necessary to practice the method of this invention.

A DETAILED DESCRIPTION Referring now to the drawing, the basic elements making up the apparatus necessary to practice the invention are shown. The invention is a method of providing drilling fluid for drilling a bore hole 10 in the earth as is required for drilling oil and gas wells. The hole 10 extends from the surface 12 of the earth and is drilled by the customary procedure of rotation of a drill string 14 in hole 10, the drill string 14 having a rotary `bit 16 at the lower end thereof. The bit 16 engages the earth at the bottom of hole 18 and the rotation of the bit 16 under compression chips away the earths formation. Chips produced by the bit 16 must be transported from the bottom of the hole to the earths surface 12 and this is a primary function of a drilling medium. In addition, bit 16 must be cooled and lubricated to insure the life thereof.

It has long been a procedure in the petroleum industry to force a drilling medium down the interior of the drill string 14, the drilling medium passing out at the bottom of the hole through bit 16 and back up the annulus 20 between hole 10 and the exterior of the drill string 14. This known procedure is utilized whether the drilling medium is a liquid base material or air.

A kelly indicated by the numeral 22 is used as a means of rotating the drill string 14 and at the upper end of the drill string is a coupling 24 which rotatably receives the drill string and permits a drilling medium to be injected in the top thereof into the interior of the drill string.

The stiff foam drilling medium of this invention is made of two basic components, that is, a liquid foam mixture and air. The liquid foam mixture is made up of two basic portions, that is, a liquid foam base medium which is stored in chemical tank 26, and a foaming agent which is stored in foaming agent tank 28. The liquid foam base material from tank 26 is injected by way of conduit 30 into an injection tank 32. At the same time the foaming agent is injected by a proportioning pump 34 and conduits 36 into the injection tank 32 where the foaming agent is mixed with the liquid foam base material.

From the injection tank 32 the liquid foam mixture passes by way of conduit 38 to an injection pump 40 actuated by engine 42. The liquid foam mixture passes from injection pump 40 by way of conduit 44 into conduit 46 having communication with the rotary coupling 24 whereby the drilling medium is injected into drill string 14.

Concurrently with the injection of the liquid foam material, air from compressor 48 driven by engine S0 is forced through conduit 52 and into the injection conduit 46. In injection conduit 46 the air and the liquid foam mixture are intimately mixed causing the formation of a stiff foam vdrilling medium. The pressure of air from compressor 48 and the pressure of the liquid foam mixture from injection pump 40 are adjusted to be suchy as to force the stiff foam material down the interior of the drill string 14, out the bit 16, and up the annulus 20` to the earths surface.

The proportioning pump 34 may be driven by a separate engine or by auxiliary shaft 54 from engine 42.

For effective removal of cuttings to insure consistent drilling rates, the volume of foam drilling medium must be maintained at a substantially constant level. An orifice plate 56 is positioned in conduit 52 to detect the rate of flow of air passing through conduit 52. The differential pressure across the orifice plate 56 is transmitted by way of pipes 58A and 58B to a transducer 60 wherein the flow rate of air passing through conduit 52 is converted into an indicating signal, the signal in turn being fed into a computer 62 through conductor 64. The computer in turn provides an output signal on conductor 66 which opens and closes a solenoid valve 68 in conduit 70. When solenoid valve 68 is open air is vented to the atmosphere. In this way the valve 68 regulates the volume of air passing through conduit 52 thereby maintaining a constant rate of flow of air into the drill string 14 in an arrangement wherein the engine 50 may be driven at a constant speed.

The liquid foam base medium utilized in this invention preferably consists of 1200 pounds of bentonite, 100 pounds of soda ash, 100 pounds of guar gum and the balance of water sufficient to make 5500 gallons. The -foaming agent is added at the rate of one percent of the liquid foam base medium. The foaming agent may be any commercially available detergent.

The approximate air volume required in the stiff` foam drilling medium of this invention can be computed by the following formula: V: (D2 .7854).868 Where V is the air required in cubic feet per minute and D is the bit diameter. For instance, a 6% inch bit requires approximately 26.63 cubic feet of air per minute and a 9 inch bit requires approximately 55.22 cubic feet of air per minute.

While this invention has been described with a certain degree of particularity, it is manifest that many changes may be made in the steps composing the method of this invention without departing from the invention. It is understood that the invention is not limited by the abstract, nor the summary, nor the specific embodiment by which the method of the invention may be practical Which is illustrated herein for purposes of exemplication only, but the invention is to be limited to the following claims, including the full range of equivalency to which each step thereof is entitled.

What is claimed is:

1. The method of providing a drilling fluid for use in drilling oil and gas wells, the drilling uid being forced down the interior of a drill string, ejected through a bit at the lower end of said string and returned to the earths surface through the annulus between the bore hole and the exterior of said string, comprising the steps of injecting a liquid foam mixture into a conduit having communication with the interior of said drill string; compressing air at a substantially constant rate; directing the compressed air to a valve controlled atmospheric discharge and simultaneously into said conduit containing said liquid foam mixture to intimately mix said air and liquid to provide a stiff foam drilling medium; continuing to inject said liquid foam mixture and air into said conduit and therefrom into said drill string and up said annulus to the earths surface, the foam drilling medium serving to cool and lubricate the drill bit and carry cuttings out of the drilled hole; detecting the rate of flow of air into said conduit; and regulating said valve controlled atmospheric discharge to discharge air to the atmosphere at a rate so as to maintain a substantially constant rate of flow of air into said conduit and thence into said drill string. 2. A method according to claim 1 wherein the step of detecting the rate of flow of air into said conduit includes passing the air flowing through said condnuit through a venturi to create a pressure differential thereacross, and wherein the step of regulating said valve controlled atmospheric discharge includes converting the pressure differential across said venturi into a flow indicating signal and conducting said flow indicating signal to said valve controlled atmospheric discharge. 3. A method to claim 1 wherein air is injected into said drill string at a rate at least equal to that given by the formula where V is the volume of air in cubic feet per minute and D is the diameter of said bit.

References Cited UNITED STATES PATENTS 2,818,230 12/1957 Davis 175-69 3,130,798 4/ 1964 Schramm et al 175-69 3,313,362 4/1967 Schneider 175-71 JAMES A. LEPPINK, Primary Examiner IAN A. CALVERT, Assistant Examiner U.S. Cl. X.R. 

